Composition for coating engraving-plates



U ITED STATES PATENT OFFICE.

THOMAS H. BELL, OF CLEVELAND, OHIO.

COMPOSITION FOR COATING ENGRAVlNG-PLATES.

SPECIFICATION forming part of Letters Patent No. 626,016, dated May 30, 1899.

Application filed August 18, 1898. Serial No. 688,848. (N specimens.)

To all whom it may concern:

Be it known that I, THOMAS H. BELL, a citizen of the United States, residing at Cleveland, in the county of Cuyahoga and State of Ohio, have invented certain new and useful Improvements in Composition for Coating Engraving-Plates; and I do declare that the following is a full, clear, and exact description of the invention, which will enable others skilled in the art towhich it appertains to make and use the same.

My invention relates to a compositionfor coating engraving-plates.

It is well known to those familiar with this art that much of the picture-work now so popular in .our daily and weekly newspapers is first wrought out by an engraver with a suitable tool on coated plates, from which stereotypes or electrotypes are made. The plates themselves usually employed for this purpose are either of blue steel or glass, but may be of any like material, and they are designed to be used over and over again after casts have been taken therefrom and they have been cleansed by removing the coating. The coating used always is of some friable composition or combination of materials in which a dry and powdered base, generally of an earthen character, is united by a bond which will bind the particles to each otherand to the base-plate and when dried orf baked will enable an engraver with a simple 5 tool to produce in or upon said coating a matrix from which the casting or molding is taken. thin, but evenly distributed over thevplate, and needs to be of sufficient firmness and coherence to withstand the action of the tool without breaking down injuriously between the lines and to endure casting in the subsequent steps of development, as hereinbefore described. v

To obtain firmness and coherence of the coating and the necessary adhesion to the plate itself, a number of different bonds or ingredients have from time to time been employed and some with more or less success, notably the silicates or soluble glass, which probably has been the most common and satisfactory but I have discovered a bond which so far as I know and believe has never before This coating always is comparatively 1 been known or used and which I believe to be not only new and original with me, but of very superior quality for this purpose. I therefore give the following formula for producing my new and improved coating: English precipitate of chalk, eight ounces; French chalk, four ounces; sulfate of barytes, two ounces; gum-arabic, one-half ounce pure albumen, (white of egg,) one-half ounce. The earths or earthy substances named in this formula are of course old and well known in coatings for engraving-plates, as they were used many years ago, as were also different kinds of chalk not here enumerated, plaster-of-paris, clay of one kind and another, and so on, and to these parts in themselves or their equivalents I lay no present claim; but the gum-arabic and the pure albumen together as a bond and in conjunction with the other elements of the formula to make a coating for'engraving-plates I do lay claim to as new and essentially as my invention; but while I have given a defi nitely-stated formula both as to materials and quantities it will be understood that I do not necessarily confine myself exclusively to these materials, except in the matter of the bond,whichis definite and exclusive and is not to be varied in character or materially in the relative proportions stated; but the earths employed as a base obviously may be substituted by their equivalents and be varied more or less in their proportions without materially departing from the invention. So, also, in the bond itself, while the proportions above given are found to be entirely satisfactory 1 have found that I canalso get very good results by using a little more or a little less of the pure albumen, while at the same time I decrease or increase the proportion of gum-arabic-correspondingly, and hence variation of these ingredients of the bond between themselves may be permitted within careful limits and yet make a satisfactory coating.

In the preparation of the coating the most ing added in any case to give the mixture the desired consistency. If the gum-arabic be in mass or pieces, it should first be dissolved, preferably with warm water, and then mixed with the other ingredients. Any suitable vessel can be employed for this purpose and any steps taken to incorporate the elements with each other that may be preferred, so that at last a smooth pasty consistency is obtained. Then it is applied to the plates in the usual way.

It is well known to artists that a plate bonded entirely with gum-arabic is not suitable for free-hand drawing or capable of standing the fine work necessary to finish a complete work of art. Gum-arabic, when used by itself on metal or steel plate, breaks away in large pieces, but when used on a porous base-such as paper, cardboard, or rough slate or the like-it makes a good binding agent. For that reason gum-arabic can only be used successfully when incorporated with an ingredient which will give it a softening action upon the surface and which gives it more binding properties when it comes in contact with a hard surface, in that way binding the particles of chalk more closely to the base-plate than they are bonded to each other. Gum-arabic also, when used as a bond, causes rust to gather, which destroys the effect of the picture, as when the artists etching-point comes in contact with a fleck of rust it causes the point to swerve from its course, and thus destroys the drawing; but with a combination of albumen it removes all possible chance of rust accumulating upon the base-plate, because the albumen secures the plate against rusting. I also find that the use of albumen in combination with gum-arabic renders the plate practically proof against dampness, which is a very material advantage.

I have found that albumen cannot be successfully used alone as a binding agent for a chalk engraving-plate. If used alone, it will rise in spots from the base-plate by the action of the heat and also become very porous, so that an even and true line cannot be drawn upon the plate. Of itself it is too light and rises to the surface of the mixture, causing the upper part or strata of the plate to become brittle, so that a good plate cannot be made from using albumen as a bond by itself.

that I claim as new, and desire to secure by Letters Patent, is

1. A coating for engraving-plates comprising suitable chalks as a base, and a bond containing albumen and gnm-arabic substam tially as shown and described.

2. The coating, substantially as described, comprising an earthy base and a bond containing gum-arabic and substantially pure albumen in the proportions substantially as described.

3. A new composition of matter for coating engraving-plates, consisting of a base of mineral substances and a bond of pure white of egg and gum-arabic combined in the propertions substantially as described.

4. The herein -described composition of matter consisting of chalk, sulfate of barytes, pure albumen and gum-arabic, in the propertions substantially as described.

Witness my hand to the foregoing specification this Elth (lay of August, 1898.

THOMAS II. BELL.

\Vitnesses:

R. B. MosER, H. E. MUDRA. 

